Selective xerographic fuser



July 7, 1970 G. A. ASER ET AL 3,519,253

SELECTIVE XEROGRAPHIC FUSER Filed Oct. 11. 1966 4 Sheets-Sheet 1 INVENTORS GILBERT A. ASER GEORGE D. DEL VECCHIO JOHN A. HALLAGAN BY EDWARD A. SCHWARTZ i Q A A T TORNE) July 7, 1970 G. A. ASER ET AL 3,519,253

. SELECTIVE XEROGRAPHIC FUSER Filed Oct. 11, 1966 4 Sheets$heet 2 TEMP.

CONTROL.

INVENTOPS GILBERT A. ASER GEORGE D. DEL VECCHIO JOHN A. HALLAGAN y EDWARD A. SCHWARTZ FIG. 2

A 7' TORNEV July 7, 1970 A. ASER ET AL SELECTIVE XEROGRAPHIC FUSER 4 Sheets-Sheet 4 Filed 001;. ll. 196$ RONZ L E A- m 5 G mAmAA .V, T LW E w N MT Ac RLHS 0 V E T M NW .A qmm Q R 0 E4 E G US. Cl. 263-6 4 Claims ABSTRACT OF THE DISCLOSURE A xerographic heat fusing system for selectively heat fusing toner images above a predetermined density in the presence of less dense images without fusing said less dense images. An image bearing supporting material is electrostatically tacked image side up on a movable heated surface and the temperature of the surface accurately controlled to slightly below the fixing temperature of the toner so that the support material is rapidly heated to approximately the temperature of the movable surface. The surface and the image bearing support material are moved into thermal communication with a radiant energy source emitting energy concentrated about a wavelength at which the toner is highly absorptive and at which the support material is relatively non-absorptive. The temperature of the support material remains stable during the fusing process wherein the support acts as a heat sink controlling the selectivity of the fusing system.

This invention relates to apparatus for fixing a xerographic powder image and, in particular, to apparatus for heat fusing a xerographic powder image.

More specifically, this invention relates toan improved radiant fuser capable of fusing resinous powder images of relatively low density. In the process of xerography, a plate comprising a photoconductive insulating coating on a conductive backing is provided with an electrostatic charge and then exposed to a light image whereupon the coating becomes conductive under the influence of light so that the electrostatic charge is selectively dissipated to produce a latent image. The latent image is developed by means of a variety of pigmented resins that have been specifically developed for this purpose. The resins or toners are electrostatically attracted to the latent image on the plate in proportion to the amount of charge found thereon or therein so that the areas of small charge concentration become areas of low toner density while areas of greater charge concentration become proportionally more dense. The developed image is then transferred to a support material and permanently fixed; the application most generally employed being to transfer the image to a paper support and heat fixing the toner to form a bond with the paper fibers.

Selective fusing, as herein used, is the fixing of toner areas of a higher density to the exclusion of relatively low density areas. However, selective fusing hasproven to be a rather difficult method of heat fixing image areas of low toner concentration. That is, it has been found that these areas of low density are unable to absorb sufficient energy to be properly fused in the relatively short time permitted in automatic xerographic machines. Attempts to deliver more energy to the areas of low toner concentration by increasing the intensity of the infrared energy during the access time have caused the support material to be damaged before proper fusing is accomplished. Further, the images of high density concentration absorb an excess of this high intensity energy causing them to literally explode or burn through the paper support before the areas of low concentration are fused.

United States Patent 3,519,253 Patented July 7, 1970 "Ice Ideally, what is desired in a xerographic heat fusing process is to bring the temperature of the support material as near as possible to the fusing temperature of the xerographic developing powder so that the paper support acts more as a heat source than a heat sink during the fusing operation. However, high intensity infrared radiation which is produced at the shorter wavelength favors the absorptive qualities of the toner over the paper support so that it is impossible to radiantly produce the same temperature in both materials within a short fuser access time.

Pre-heating of the paper support material before exposing the toner to infrared radiation has been tried in an elfort to eliminate some of the heretofore mentioned problems associated with rapid selective infrared fusing. In Toku Hojo et al., US. Pat. No. 3,187,162, a web of image bearing paper is moved over a heated platen so that sufficient heat is transferred to the paper by conduction to aid in a selective fusing process. However, in high speed Xerographic machines a highly eflicient conductive heat transfer is required in order to heat the support material within the relatively short access time allowed to accomplish selective fusing. Rapidly moving a support material over a heated platen produces boundary layers of air between the support and the platen which prevents this rapid and efiicient conductive heat transfer. The more rapid the speed at which the support is moved over the platen, the more formable becomes the boundary layer. It can be seen that the amount or scope of selectivity is severely limited by these boundary layers because of the lack of control over the conductive heating of the paper because of gaseous boundary layers.

The type of support material most processed in xerographic machines is sheet paper which is pre-cut to the size of legal documents, ledgers, invoices, and the like which are in wide general use. Moving such a relatively small, non-rigid, sheet rapidly over a heated platen without creating a boundary layer between the two surfaces is extremely difficult if not impossible. The leading edge of a rapidly moving piece of paper acts much as the bow of a boat in that a boundary layer of air and/or gas is forced around the paper. As can be seen, the more rapid the movement of a cut paper sheet over a heated platen, the greater will be the boundary layer created.

Controlling the temperature to which the paper is preheated has heretofore also been a problem because of the many uncontrolled variables associated with the heat transfer problem. For example, the rate at which heat is loss to heat sinks such as paper handling equipment or the like found in the fuser zone has been impossible to predict. Changes in the moisture content of the support material have also proven to be unpredictable variables which enters into the pre-heating problem. That is, as the moisture content of the paper varies, the amount of conductive heat dissipated in driving off moisture will also vary.

It is therefore an object of this invention to improve apparatus for heat fixing a toner image to a paper support material.

It is a further object of this invention to precondition cut sheet paper prior to radiant heat fusing a Xerographic powder image found thereon.

It is another object of this invention to rapidly and efficiently heat fix xerographic images of varying densities using infrared energy.

Another object of the present invention is to selectively fuse low density toner images.

A still further object of this invention is to rapidly and efficiently heat fix xerographic images of varying densities to a support comprising a sheet of pre-cut paper material.

A still further object of this invention is to provide a xerographic fuser for rapidly heat fixing toner images on a pre-cut paper support for use in a highspeed automatic xerographic machine.

Yet another object of this invention is to provide heat fusing apparatus for processing cut paper material having a minimum of heat sinks present in the fusing zone.

These and other objects of this invention are obtained by accurately controlling the temperature of a cut paper support material so that toner images of varying densities, which are loosely adhered thereto, are able to be rapidly and efficiently fused by infrared energy.

For a better understanding of the present invention as well as other objects and features, thereof, reference is had to the following detailed description of the invention to be read in conection with the accompanying drawings, wherein:

FIG. 1 illustrates schematically an automatic xerographic reproducing apparatus using a preferred embodiment of the heat fuser of the present invention;

FIG. 2 is a partial sectional view of the heater fuser roll shown in FIG. 1;

FIG. 3 is a plot of the parameters important in xerographic radiant heat fusing against wavelengths on which are superimposed the infrared characteristics of the apparatus shown in FIG. 1;

FIG. 4 is a side view of the environmental control of the present invention with portions broken away to show internal operations of the apparatus.

In a high-speed xerographic machine, very little access time is available in which to selectively heat fuse a toner image to a support material and, therefore, a rapid and efficient heat transfer must be accomplished. Radiant heat transfer in which infrared energy is emitted from a high temperature source in the form of electromagnetic waves provides an eflicient source of energy which can be readily transferred from the source to a receiver. However, this energy must be capable of being absorbed rapidly by the receiving material, that is, the body receiving the energy must rapidly absorb a high percentage of the energy incident upon its surface. xerographic powders, or as herein referred to as toners, are capable of rapidly absorbing about 94% of all infrared radiation incident thereon regardless of the wavelength at which the energy is traveling. It can be therefore be said that xerographic toner acts as a black body in that it is highly receptive to infrared heat energy.

However, it is difficult to radiantly heat fix areas of low toner density because a relatively small surface area is presented through which radiant heat energy can be absorbed. Further, relatively little of this absorbed heat I energy can be stored internally in areas of low density because the toner mass of the image is also small. It has been found that by increasing the intensity of the infrared radiation to a point where low density fusing is obtained has the effect of causing excessive heating in areas of high toner concentration leading to toner explosions and/ or images burning through the paper.

As noted, xerographic developing powders are known to act as black bodies in trat they will absorb a high percentage of all infrared energy regardless of the wavelength. However, an efficient radiator of infrared energy, that is a radiator that converts a high percentage of the internal energy available to radiant heat, will concentrate this energy in a narrow band of wavelengths located at the short end of the infrared spectrum. For instance, a tungsten filament, which is considered a good source of infrared radiation, converts about 86% of the internal energy available to infrared energy when operating at a temperature of approximately 4,000" P. and the energy so produced being concentrated with a narrow band of wavelengths centered about 1.1 microns A plot of the various parameters of importance to the xerographic infrared fusing process are shown superimposed on a single graph in FIG. 3. The curves are a plot of energy level against wavelengths and are based upon a percent of a theoretical energy level so that the parameters can be visually compared. It can be seen that paper absorbs a high percentage of infrared energy at wavelengths greater than 3.0 microns but the absorption curve falls off rapidly in respect to infrared energy found at the shorter wavelengths. In contrast, the absorption of xerograaphic powder or toner is relatively constant in that the toner absorbed over of all infrared energy it receives regardless of the wavelength. It should be particularly noted that the radiation emission curve for a high temperature radiation source operating at 4,000 F., the range of a high temperature quartz lamp, shows that a high percentage of the useful energy propagated is concentrated at a wavelength at which paper has extremely poor absorption characteristics. A comparison of the three curves clearly points out that the high efiiciency infrared energy produced at the shorter wavelengths is readily absorbed by the xerographic powder but has little or no heating affect upon xerographic paper.

As shown by the graph in FIG. 3, infrared energy which is incident upon a toner image is rapidly converted to internal energy. However, when the temperature of the support material is lower than that of the toner image, the support will act as a heat sink to pull heat away from the image areas. The larger the temperature difference between the tWo materials, the more heat energy that will be transferred by conduction from the toner to the support. As can be seen, the heat drain in areas of low toner density will be critical .because any small heat drain upon the limited internal energy available can mean the difference between a fuse and a no-fuse condition.

In the present invention, the use of a high temperature infrared source is made possible as a means to rapidly fuse low density images by pre-conditioning the paper support material. Apparatus is provided for accurately controlling the temperature of the support material which in effect, controls the heat drain away from the lowdensity image areas. That is, the higher the paper temperature, the less will be the conductive heat drain from the low-density image areas thus resulting in more available energy in areas of smaller concentration.

Referring now to FIG. 1, the present invention is shown embodied in a high-speed xerographic machine. Cut sheets of bond paper are deposited in tray 10 prior to delivery into the machine. The paper tray not only supplies the machine with support material but also aids in pre-conditioning of the paper prior to infrared heat fusing. The tray is provided with both a temperature and humidity control which are capable of maintaining the moisture content in the paper support material within a desired level. Moisture content of the paper is one of the many variables which, if left uncontrolled, leads to erratic and oftentimes unsatisfactory heat fusing. Although bone dry paper is undesirable because of the danger of fire in the fuser zone, excessive moisture is also undesirable because heat energy is dissipated in driving off moisture rather than pre-heating the paper. When the access time is short such a waste cannot be tolerated.

Referring now to FIG. 4, paper tray 10 is shown in further detail. Located within housing 79 is table 81 which is secured in a movable frame 83. Rollers 82 enable the table to be raised or lowered along guide rails 78 mounted in the frame. As paper is fed from the top of stack 80, pulley 84, acting through cable 85, is rotated to move the table upwardly thus maintaining the top of the paper stack at a relatively constant level. 'In operation, a sheet sensor (not shown) rides on top of the paper stack and is capable of moving between two actuating switches electrically connected to a drive motor (not shown) operating pulley 84. When the sensor detects a low stack, by actuating the lowermost switch, the motor is started causing the pulley system to raise table 81 to the desired operating level. When the operating level is reached a second motor cut-off switch is actuated by the sensor causing the motor to stop. Adjustable guide 87 permits loading of cut paper sheets of varying sizes as well as properly aligning the leading edges of the sheets in the paper stack.

A suction foot 90 communicates through a hollow tube with a manifold system capable of producing a negative pressure at the foot. A cam system acts in conjunction with the suction foot to take paper from the stack and place it into the bite of drive roller 91 and pinch roller 92 of vacuum support system 12. A rocker arm 94 is mounted in shaft 95 which being driven at synchronous speed with the xerographic apparatus shown in FIG. 1. Rocker arm 94 in turn is employed to drive cam follower 96. Cam follower 96 acting through linkage 97 moves the suction arm upwardly and, at the same time, forward so that a paper sheet held thereon is moved into the bite of the transport rollers. For further information concerning a suitable vacuum feeding apparatus, reference is had to J. W. Wagner, Pat. No. 3,241,830.

By controlling the environmental condition of the atmosphere found within housing 79, the moisture content of the paper stored therein is maintained at a desired level. In operation, humidistat 100 continually monitors the moisture content of the environmental atmosphere within housing 79. When the moisture content of the atmosphere rises above a described level, heat energy is added to the atmosphere thereby reducing the relative humidity found therein. That is, heat energy is added to the vapor mixture to raise the temperature to a point where a psychrometric spread between the dry bulb and wet bulb temperatures of the atmosphere produces a relative humidity within the desired limits or, in other words, the temperature is raised without the addition of more vapor to reduce relative humidity. Heat energy is added to the environmental atmosphere by means of heating pads 102 and 103, respectively, located in the top and bottom of housing 79 and controlled by means of thermostat 101.

To further insure that the paper sheets in the stack are properly conditioned, dry hot air is blown around the sheets prior to delivery to vacuum transport system 12. Compressed air is forced into heating chamber 105 through means of tubing 106 where it is heated to the desired environmental level. The amount of heat conductively transferred within the chamber to the air is regulated by thermostat 107 which again is operating in conjunction with, and controlled by, humidistat 100. The heated air is passed to a manifold system 108 which then delivers it to front paper flufler 109 and side paper fluifer 110. The fluffers are positioned within the housing in relation to the paper stack so that hot gases are blown through the uppermost sheets in the stack thereby subjecting the entire surface areas of the sheet to controlled environmental atmosphere before delivery into the xerographic apparatus shown in FIG. 1.

On demand, cut paper is transported by means of vacuum transport system 12 to the xerographic transfer station 15. The paper is aligned by registry device 14 and then moved into contact with xerographic drum 13. Drum 13, which is moving at the same peripheral speed as transport 12, has placed upon it a latent image which has been developed by means of xerographig developing powder. The powder image is transferred electrostatically to the paper support by exposing the back of the paper, or the side not in contact with the toner image, to an ion discharge from transfer corotrons 16 which is of sufficient strength to attract the image from the drum to the paper. After transfer, the image bearing support is removed from the drum by means of air puffer 18 and placed image side up upon vacuum belt transport system 19.

The cut paper support material, having a toner image loosely adhered thereto, is moved into contact with a heated roll 20 by means of belt transport 19. Belt transport 19 is placed at a relatively steep angle in reference to the horizontal plane and acts in conjunction with curvilinear guide member 21 so as to crimp or arcuate the paper being transported thereon. Placing the paper in a bowed configuration pre-stresses the paper so that it possesses sufiicient rigidity to be forced into intimate contact with the heated roll 20 under the driving action of transport 19.

Conductive heating of a paper support is accomplished in the present invention by electrostatically tacking the paper material into intimate contact with heated roll 20'. Electrostatically tacking the paper to the roll eliminates any boundary layer of air or gas which might form between the heated surface and the paper support. The roll, which is being maintained at a constant temperature, supplies heat directly to the paper at a constant controllable rate. That is, by knowing the temperature of the heat source and the temperature of the paper support, which has been pre-conditioned in paper tray 10, the rate of heat transfer between the two bodies can be readily determined. By varying the temperature diiference between the two bodies, the rate of heat transfer can be controlled to bring the temperature of the support material just below the fusing temperature of the toner.

As shown in FIG. 2, heated roll 20 is rotatably mounted in frame 25 and is being driven at the same peripheral speed as transport 19 by means of drive motor 26 (FIG. 1) acting through sprocket 27. Basically, the roll is constructed of a metal cylinder 30 upon which is placed a coating 29 capable of acting as an electrical insulator. Preferably, the coating is of tetrafluoroethylene, marketed under the trade name Teflon, which is known to have excellent release or adhesion characteristics at high temperature as Well as giving relatively good heat transfer properties. Cylinder 30 is fabricated of copper, aluminum, or any other metal which has good heat transfer characteristics.

The arcuated paper support material is driven into intimate contact with the Teflon surface of the roll with the image side up. The paper is then electrostatically tacked to the Teflon surface by exposing the paper to a spray of charged ions emitted from tacking corotron 28. A pre-conditioning corotron 31, shown in FIG. 1 posi tioned forward to the point at which paper contacts roll 20, prepares the insulated surface to receive the paper. The pre-conditioning corotron generates a corona discharge of opposite polarity to that generated by the tacking corotron and places this charge upon the insulating surface of the roll. The opposite charge will, in the first instance, negate any unlike charges remaining on the roll which would tend to repel the tacked paper support. Also, the pre-conditioning corotron provides an additional force to aid in more tightly holding the paper support in intimate contact with the roll. That is, an oppositely charged field is placed on the insulator surface prior to paper contact thereby providing a field capable of attracting ions emitted by the tacking corotron thereby producing a substantial force capable of holding a cut paper support in intimate contact with the roll.

Referring once again to FIG. 2, heated roll 20 has a heating element 35 mounted along the axial center line of the roll which is electrically connected to a temperature control 33. Metal cylinder 30 is closed at each end by means of caps 31 and 32 in which are seated bearings about which the roll rotates. An exhaust line 37 is mounted on machine member 24 and is in communication with air chamber 36 formed by the hollow cylinder and hollow shaft 38. Exhaust line 37 is operably connected to a motor driven vacuum pump 34 which is capable of pulling ambient air through air chamber 36. A constant supply of relatively cool ambient air is supplied to the chamber through means of a plurality of air ports 39 machined in cap 32.

A constant control of the temperature found at the surface of roll 20 is maintained by means of thermistor 40 (FIG. 1) acting in conjunction with heating and cooling means within said roll. Thermistor has a heat sensing probe which is biased into contact with the surface of the heated roll. Biasing is accomplished by a weighted lever arm which causes the probe to apply substantially equal pressure to the roll surface regardless of roll-out or other unbalancing forces. Because the biasing pressure is constant, the heat caused by friction will also be constant. By allowing for this heat of friction, an accurate measurement of the temperature at the surface of the heated roll is obtained.

In operation, thermistor 4t) accurately senses the temperature at the surface of the roll and electrically sends its findings to temperature control 33 which has been preset to a desired temperature. If it is electrically sensed that the surface of the roll is above the desired temperature, the vacuum pump is actuated which in turn moves relatively cooler ambient air through the roll until equilibrium conditions at the surface of the roll are again restored. Likewise, if the thermistor senses that the surface temperature of the roll is beginning to cool, heated element 35 is enabled thereby raising the temperature of the roll once again to the desired equilibrium temperature. It can be seen that the temperature at the surface of the roll is not only constantly monitored but also accurately controlled which, in turn, acts to control the rate at which a paper support tacked to the roll received heat energy.

Referring once again to FIG. 1, a source of infrared radiation 42 is shown mounted above, and in thermal contact with, the heated roll 20. Radiator 42 comprises a high temperature quartz lamp mounted in a reflector assembly 43 about which is placed a manifold system 44. The reflector assembly 43 has a relatively narrow opening positioned above and running longitudinal with respect to the roll. The reflector concentrates the infrared energy from the radiation source along a relatively narrow portion of arc along the surface of the roll. The inner surface of the reflector is coated with a material having high reflectivity as well as good heat stability, as for example gold, aluminum, or the like. Manifold system 44 is provided to remove gases created during the fusing process from about the reflector assembly. It has been found that the waste gases given off by the fusing process collect in the dish-like reflector and eventually form a film on the reflector surface reducing reflectivity and thus reducing the elfectiveness of the infrared fusing. A series of manifold ports are positioned adjacent to the reflector in housing 44 running longitudinal in reference to heated roll 20. Gases from around the infrared fuser assembly are continually exhausted from the system through means of these ports thus preventing the heretofore mentioned film buildup on the reflector surface.

As heated roll 20 rotates in the directed indicated in FIG. 1, the pre-conditioned paper, which is tacked to the roll image side up, is brought into thermal contact with the infrared radiation being emitted from the high temperature quartz lamp. The energy propagated by the lamp, concentrated at the shorter wavelengths, is at an intensity level capable of rapidly and efficiently heating xerographic toner of varying densities. A

The cut sheet of paper, tightly adhering to roll 20, 1S removed from the roll by means of pick-off arm 65. The arm is pivotively mounted adjacent to the roll on machine member 70 and is free to ride in slot 67 provided in roll 20. Arm 65 is tapered to a point and positioned so that the point rides below Teflon surface 29 enabling it to engage the underside of the cut paper support thereby stripping the paper from the roll. As the paper is being stripped from the roll, it is driven forward along baflles 68 into contact with vacuum transport system 52 (FIG. 1). A support arm 69 is shown in FIG. 2 mounted to baflle plate 68 and is provided to prevent the paper support from buckling as it is driven along baflle 68 into contact with the transport system.

A Teflon wick, which is impregnated with silicone oil,

is positioned at a station subsequent to the paper stripping station. The Teflon wick is mounted in housing 75 and is capable of contacting the Teflon surface of roll 20. It has been found that residual toner found in the machine will, under certain conditions, be attracted to an insulated surface such as Teflon. Residual toner adhering to the roll would prevent intimate tacking of the support material to the roll and thereby create the heretofore mentioned unwanted boundary layers. As the roll rides over the wick any toner that may be adhering thereto will be removed. Further, the wick places a thin layer of silicone oil on the Teflon roll which acts to impede a toner buildup thereon.

Referring once again to FIG. 1, fused copy is vacuum transported beneath brush assembly 50 where residual or unfused toner is removed from the support material. Brush 51, which can be fabricated of synthetic or natural fibers, is mounted in respect to transport 52 so that some interference exists between the paper support material and the brush fibers. Rotating the brush at a relatively high speed in a direction opposite to that of the paper removes unfused residual toner often referred to as background. Residual toner so removed is exhausted by means of a vacuum system maintaining a negative pressure under hood 53. The fused and brushed cut paper support is then vacuum transported to receiving bin 61 by means of transport system 60.

It should be noted that selective fusing is enhanced in the present invention by properly conditioning the support material. By pre-conditioning the paper support material so that image areas of a desired toner density found thereon can be rapidly and efliciently fused by highly eflicient infrared energy found at the shorter wavelength. Pre-conditioning consists of controlling the moisture content of the paper support material and conductively heating the support material to a desired level whereby the support material acts as a controllable heat sink. Moisture content of a paper support is known to vary from day to day with changes in the ambient air conditions and, if left uncontrolled, would seriously effect selective fusing. That is, fusing would vary as the conductive heating of the paper varied due to moisture changes.

Rapid and eflicient conductive heating of the paper support is made possible in the present invention by removing all unnecessary heat sinks from the fuser area, and eliminating all boundary layers between the conductive heat source and the support material. Electrostatically tacking a paper support material or the like to a heated Teflon roll or the like eliminates the boundary layers which severely impede the conductive heat transfer as well as eliminating bulky paper handling devices. Because the temperature of the support material is rapidly and efficiently raised to a level where the paper drains little heat from the toner, infrared energy of an intensity that is economically feasible can be utilized to selectively fuse xerographic image. Therefore, by closely controlling or eliminating the heat transfer variables it is possible in the present invention to selectively fuse low density images such as found in half tone or continuous tone images over unwanted background in a high speed automatic xerographic machine. The unwanted and unfused background can be easily removed by brushing or the like to produce excellent copy.

In an automatic xerographic apparatus similar to that shown in the preferred embodiment, 6.66 inches per second of pre-cut paper is pre-heated to a temperature of 220 degrees F. in approximately 0.5 second on a heated roll. The preconditioned paper support is transported past the infrared source at a rate so that thermal contact of about 0.02 second is had in which fusing is accomplished. It is found that this relatively short access time is suflicient to fuse line copy having moderate and high density images thereon when operating the infrared source at approximately 1,700 watts. Likewise, the access time allowed is sufiicient to rapidly and efiiciently fuse low density half tone or continuous tone images when 2,500 watts of power is supplied to the infrared source. It should be noted, that the change in input power regulates the intensity of the infrared energy produced by the source but has relatively little or no effect on the wave length and relative distribution of the energy so produced making it possible to utilize most commercially available infrared lamps in the present invention. It is therefore feasible and desirable to have two modes of operation in this type of apparatus. A first mode in which a lower power setting for reproducing moderate and dense images, such as line copy or the like, is available and a second for reproducing half tones and the like at a higher power input to the infrared source.

While this invention has been described with reference to the structure disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the scope of the following claims.

What is claimed is: 1. In an apparatus for selectively heat fixing a heat fusible image to a cut sheet of final support material of the type comprising means to first preheat the support sh :et and a radiant source of energy emitting energy concentrated about a peak power wave length at which the support sheet is substantially non-absorptive and at which the image is highly absorptive for fusing the image to the sheet, the improvement comprising said means to preheat the sheet comprises a movable member positioned to move in a path through a sheet receiving station and a radiant fusing station,

means to place the non-imaged side of the cut sheet of final support material in contact with the outer surface of said member,

means positioned adjacent to the sheet receiving station to electrostatically tack the cut sheet of final support material in contiguous relation with the surface of said member to eliminate gaseous boundaries therebetween,

means to move said member and said image bearing support material tacked thereon into thermal communication with said radiant heat source for a predetermined period of time,

sensing means to detect the surface temperature of said member, and

means responsive to said sensing means to internally heat and cool said member to maintain the surface of said member at a constant level as the member moves into thermal communication with said radiant source wherein images in excess of a preselected density are fused to the final support sheet.

2. The apparatus of claim 1 further including means to remove said sheet from said member after the image is selectively heat fused thereto.

3. The apparatus of claim 2 further including means to remove unfused images from the support sheet after said sheet is removed from said roll.

4. The apparatus of claim 3 wherein said movable member comprises a roll being adapted to move in an endless path through the sheet receiving station and the radiant fusing station.

References Cited UNITED STATES PATENTS 2,701,765 2/1955 Codichini et al. 11721 X 2,807,703 9/1957 Roshon 11717.5 X 2,834,132 5/1958 Tayler et al. 317262 X 3,187,162 6/1965 Hojo et a1 118-637 X 3,256,002 6/1966 Hudson 117-17.5 3,349,221 10/1967 Schulze et a1 219--216 X 3,356,831 12/1967 Andrus et a1 11717.5 X 3,374,769 3/1968 Carlson 118-637 X 3,380,436 4/1968 Williamson et al. 11717.5 X 3,390,634 7/ 1968 Verderber 117-17.5 X 3,411,932 11/1968 Malone et al. 11717.5

WILLIAM D. MARTIN, Primary Examiner EDWARD J. CABIC, Assistant Examiner US. Cl. X.R. 

